Repeatability Error
24 Feb 2016 06:26 #70558
by LakshanW
Repeatability Error was created by LakshanW
Hello,
I am working on 6 axis robot arm project & now in final stage.
My teaching method is jogging and record all position values then convert it to g-code manually and run it.
I mention the my problem as follows:
Lets consider only 1st AXIS, "X" and route is A ---> B
First, i record two position values by jogging the X axis manually to point A and B. Then i make the G-code and run it.
At the first run after homing,
"A" point shift some distance and " B" also shifted in same value.
When i run it continuously, both point shifted every time.
I still couldn't find the reason for this issue.
Please reply with your recommendations.
thanks Lakshan.
I am working on 6 axis robot arm project & now in final stage.
My teaching method is jogging and record all position values then convert it to g-code manually and run it.
I mention the my problem as follows:
Lets consider only 1st AXIS, "X" and route is A ---> B
First, i record two position values by jogging the X axis manually to point A and B. Then i make the G-code and run it.
At the first run after homing,
"A" point shift some distance and " B" also shifted in same value.
When i run it continuously, both point shifted every time.
I still couldn't find the reason for this issue.
Please reply with your recommendations.
thanks Lakshan.
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24 Feb 2016 20:29 #70584
by andypugh
Replied by andypugh on topic Repeatability Error
Are you saying that the end-point shifts every time you home the machine, or every time you make the move?
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25 Feb 2016 02:35 #70595
by LakshanW
Replied by LakshanW on topic Repeatability Error
Both end point and start point shift every time when it make moves. Not only after homing. Please see the attachment.
(shifting distance is same in every time)
(shifting distance is same in every time)
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- kornphlake79
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25 Feb 2016 03:14 #70597
by kornphlake79
Replied by kornphlake79 on topic Repeatability Error
My best guess is you have a mechanical problem, possibly a coupling is slipping.
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25 Feb 2016 05:11 #70600
by LakshanW
Replied by LakshanW on topic Repeatability Error
No. I already checked it.
when it moving in shifting distance area, G-code still running. So, i confirmed this is not a mechanical error.
Other thing is i am using HD harmonic drives for joints. No any backslash.
when it moving in shifting distance area, G-code still running. So, i confirmed this is not a mechanical error.
Other thing is i am using HD harmonic drives for joints. No any backslash.
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25 Feb 2016 09:42 #70604
by andypugh
Replied by andypugh on topic Repeatability Error
Try reducing acceleration a lot (for the experiment, try reducing by a factor of 10) and see if the shift changes magnitude.
Are the motors steppers or servos?
Is the shift purely physical, or is it seen in the joint position command numbers too?
Are the motors steppers or servos?
Is the shift purely physical, or is it seen in the joint position command numbers too?
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- Todd Zuercher
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25 Feb 2016 13:43 - 25 Feb 2016 13:44 #70616
by Todd Zuercher
Replied by Todd Zuercher on topic Repeatability Error
You need to check the above things. Tell us what kind of motors you have, steppers or servos. Steppers can be very prone to missing steps and loosing position if not properly configured. Servos can lose position to, but for different reasons, that you must also trouble shoot.
If it isn't a motor positioning problem, and it isn't a mechanical problem (slipping shaft coupling...) then it may be a bug in your kinematics (this seems unlikely), and I think is why Andy was asking if your Joint positions are reading correctly. Such that if joint0 (joint1,joint2...) is commanded to move from A to B and back does it in fact do that and do the physical machine movements match what is shown in Linuxcnc. (As you probably know this is not the same as commanding a move in Cartesian space such as X0 to X2.)
If it isn't a motor positioning problem, and it isn't a mechanical problem (slipping shaft coupling...) then it may be a bug in your kinematics (this seems unlikely), and I think is why Andy was asking if your Joint positions are reading correctly. Such that if joint0 (joint1,joint2...) is commanded to move from A to B and back does it in fact do that and do the physical machine movements match what is shown in Linuxcnc. (As you probably know this is not the same as commanding a move in Cartesian space such as X0 to X2.)
Last edit: 25 Feb 2016 13:44 by Todd Zuercher.
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05 Mar 2016 19:18 #71092
by LakshanW
Replied by LakshanW on topic Repeatability Error
I am using servo motors. but not use encoder signal with LInuxCNC. and I do not use kinematics. I simply jog each axis and record position values. then make G-code accordant and run the code. actually, It was success at my first 2-3 runs. i couldn't find how its going to wrong. Any possibility of fault in my PC?
Anyway 100% sure it is not a mechanical problem. joints works without any backslash or loose.
I tried reducing the scale each axis separately. shift distance became low. not zero. But when i run the whole system at once shifting occur as earlier. confused with this.
![:( :(](/media/kunena/emoticons/sad.png)
and I observed that this problem occur due to LinuxCNC. because my machine hasn't any delay with the PC. I checked it with very slow speed. when each axis run on shifting distance linuxcnc send pulse. (g code is still running.)
Anyway 100% sure it is not a mechanical problem. joints works without any backslash or loose.
I tried reducing the scale each axis separately. shift distance became low. not zero. But when i run the whole system at once shifting occur as earlier. confused with this.
![:( :(](/media/kunena/emoticons/sad.png)
![:( :(](/media/kunena/emoticons/sad.png)
and I observed that this problem occur due to LinuxCNC. because my machine hasn't any delay with the PC. I checked it with very slow speed. when each axis run on shifting distance linuxcnc send pulse. (g code is still running.)
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05 Mar 2016 19:35 #71093
by Todd Zuercher
Replied by Todd Zuercher on topic Repeatability Error
what kind of servos? How are they interfaced with the PC?
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05 Mar 2016 19:48 #71094
by LakshanW
Replied by LakshanW on topic Repeatability Error
AC servo . i am using 3 parallel ports.
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